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Diffstat (limited to 'hello.c')
| -rw-r--r-- | hello.c | 69 |
1 files changed, 69 insertions, 0 deletions
@@ -0,0 +1,69 @@ +#include <sys/types.h> +#include <sys/socket.h> +#include <netdb.h> +#include <stdio.h> +#include <string.h> +#include <stdint.h> +#include <unistd.h> +#include <stdbool.h> +#include <fcntl.h> +#include <stdlib.h> +#include <arpa/inet.h> +#include <netinet/in.h> + +// BEEJ NETWORKING 5.1 + +int main (int argc, char *argv[]) { + + if (argc > 2 || argc == 1) { + fprintf(stderr, "Too many or not enough arguments! \n"); + fprintf(stderr, "USAGE: getip [DOMAIN]\n"); + exit(1); + } + char ipstr[INET_ADDRSTRLEN]; // We store the IP address in text form here. INET_ADDRSTRLEN is the length of ipv4 addresses. + int status; + struct addrinfo hints; // Struct where we put information in to pass it to getaddrinfo. + struct addrinfo *res; // The result of getaddrinfo. Not sure why its a pointer but ill figure that out later + struct addrinfo *rescpy; // Another rescpy struct pointer. This one is used to point to the next element when iterating in a for loop. + memset(&hints, 0, sizeof hints); // Set all values to 0 in hints. + hints.ai_family = AF_INET; // Add the necessary info to ai_family, ai_socktype, ai_flags. + hints.ai_socktype = SOCK_STREAM; + hints.ai_flags = AI_PASSIVE; + + status = getaddrinfo(argv[1], "62222", &hints, &res); // get addrinfo. Address to hints and res passed. + if (status != 0) { + fprintf(stderr, "Error: %s\n", gai_strerror(status)); + exit(1); + } + + // rescpy = res. Both point to the same result. + // rescpy != NULL. If its NULL then the next struct in the linked list is the last one. + // rescpy = rescpy->ai_next. After it did the loop it goes back, checks if its null. If not then rescpy is assigned the pointer to ai_next. And so on and so on. + // A visual representation: + // + // res --> GAI_RESULT_STRUCT (res points to the result addrinfo struct) + // rescpy = res (BOTH POINT TO GAI_RESULT_STRUCT) + // IF rescpy is not NULL + // + // rescpy = rescpy --> ai_next (Its easier for me to imagine this line with some different syntax: rescpy = rescpy.ai_next. This is technically not correct but this is for my eyes only.) + // ai_next is a pointer to another addrinfo struct. Which is the next item in the linked list. rescpy = rescpy --> ai_next, this basically means we access the ai_next member + // which is inside GAI_RESULT_STRUCT. We basically make rescpy point to the next item. + // + // + + for(rescpy = res ; rescpy != NULL ; rescpy = rescpy->ai_next) { + struct sockaddr_in *sa1 = (struct sockaddr_in *)rescpy->ai_addr; // struct sockaddr_in sa1 pointer assigned ai_addr. sa1 now points to ai_addr. + // ai_addr may be a sockaddr_in or a sockaddr_in6. + // We cast it to sockaddr_in which is supposed to just work. + void *addr = &(sa1->sin_addr); // Address of sin_addr. sa1 now points to ai_addr so we access the item sin_addr and make addr point to it. + inet_ntop(rescpy->ai_family, addr, ipstr, rescpy->ai_addrlen); + + fprintf(stdout, "%s\n", ipstr); + + } + + freeaddrinfo(res); + + return 0; + +} |